Here is a list of plugins which I use on my PSP and their functions, all tested on 5.50GEN-B2 except TweakDISPLAY which I haven't had activated for a while.
CheatMaster Fusion - PSP Cheat Device (supports CWCheat database)
CWCheat - PSP Cheat Engine
CoderPR - PSP Cheat Engine
FuSaSCR - Take screenshots (pretty fast)
Game Categories - Makes organizing games easier
Hold+ - Turns off display and underclocks CPU when you put PSP in hold mode (used for conserving power whilst playing music)
Joysens - Allows you to navigate through the XMB using the analog nub instead of DPAD.
TweakDISPLAY - A whole lot of cool XMB display effects.